Thermionic device



NOV. 24, 1936. Q JOBS-r H 2,061,733

THERMIONIG DEVICE Filed Aug. 29, 1955 l 37 32 l CATA/00E #4755 INVENTOR wmf/Z557 BY ATTORNEY Patented Nov. 24, 1936 `THERMIONIC DEVICE Gnther Jobst, Berlin, Germany,

assigner to :Telefunken Gesellschaft yfr-Drahtlose Telegraphie m. b. H., Berlin,-.Germany, vawcorporation of- Germany Application August 29, 1933, Serial No. V687,262 In Germany August 31, 1932 9 claims. (c1. 25o-27) The present invention relates, in general, to a thermionic device and more particularly to a thermionic tube and to methods of operating the same.

The primary object ofthe present invention is toiprovide Va'thermionic tube of exceedingly high internal resistance. Other objects and features will be apparent as the specification is perused in connection with the accompanying drawing.

The internal resistance Ri of a tube is characterizedl by the diierential quotient dEa y al? whereinJEs=plate Voltage and Ia=plate current and the` potentials of the other electrodes are supposed to be kept constant. `It is well known to those skilled in the art,` that the internal resistance may be increased by providing. a so-called screeny grid between the control electrode and the plate or anode of the tube. A line or close-meshed grid-L will give ahigher internal resistance than an open orwide-meshed one. But it is impossible to proceed in this wayto highv internal resistances of any desired value, as infact the plate current-decreases the finer `the meshes of the screen grid are chosen.

According tothe present invention al higher internal resistance is obtained by providing a perforatedv plateor anode and one or more' additional electrodes, which preferably arekept on constant potentials, beyond theplate. In this way the internaLresistanceRi may reach values of more than.100,000 Q or even may take negativevalues, so that the'resistance of the plate circuit Wholly or partially is neutralized.

For .'better'understanding the principle of the present finvention, the action of a tube may be consideredfwhich comprises for instance a cathode, 'afcontrol grid', a screen grid, a perforated plate ornanode and one electrode beyond the anode. .The last named auxiliary electrode is kept onfa potential less positive than the plate potential; all the electrode potentials except the control or signal grid potential may be kept constant. As the anode is perforated, not all the electrons having passed the screen grid will strike the same; a partof the electrons passes the apertures of the anode and proceeds towards the auxiliary electrode. If the plate voltage is increased the electrons are more accelerated and therefore the number of Velectrons passing the anode and falling uponthe auxiliary electrode behind the anode is increased. Referring to the plate current Is' it means, that the increase of Ia is not as great as in absence of the auxiliary electrode or, in other words, the internal resistance Ri is higher than without the auxiliary electrode.

If the density of the electron stream to the auxiliary electrode becomes sufficient a negative space charge is built up between the anode and the auxiliary electrode. Some electrons, the velocity of which is too small, are repelled by the cloud of negative particles and return to the anode, the others break through the space charge and strike the auxiliary electrode. By raising the plate voltage-the velocity of the electrons is increased so that a greater percentage breaks through the space charge. 'I'hat means, as explained above, an increasing of the internal resistance R1.

Asthe action. of the space charge is very important for the resulting internal resistance, various means maybey provided for supporting and controlling the, space charge. It is proposed to insert one` or more additional grid electrodes between the anode and the auxiliary electrode. Suppose one -grd is provided without any connection-to. another electrode or voltage source; such a grid is charged by theelectrons to a negative potential, which depends upon the insulation resistance ofthe grid and thedensity and velocity of the electronrstream. If several such insulatedor freegrids are arranged one behind another, cavities are formed bythe meshes of the grids, whereby building up the space charge is favored. Furthermore the additional grid or grids may be connected to the cathode or a negative potential. Then the desired value of internal resistance Ri is adjusted by varying the negative bias of the additional grid.

Further details regarding the tube as Well as the circuit diagram may be taken from the accompanying drawing, wherein Figure 1 represents the wiring diagram of an ampli'iier for alternating voltages according to the present invention and Figures 2 and 3 illustrate modified forms of the invention,

i InFig. 1 the input coil I, which may be connected to the aerial of a receiving station or to the plate circuit of a preceding amplier stage, induces the input voltage in the grid circuit, comprising the coil 2 and the condenser 3. The

.evacuated envelope l contains a lament 5,

which may be replaced by an indirectly heated cathode, a control grid 6, a screen grid 1, a perforated anode 8, an additional grid 9 and the auxiliary electrode I0; the latter may consist of a metal sheet or a ne-meshed wire netting. 'Ihe filament voltage is supplied by a battery Il. The' negative bias of the control grid 6 is taken from a battery I2 and the plate battery is illustrated by I4. The plate circuit contains a resonant circuit I9, 2U, which is coupled to the output coil 2i. Bypass-condensers I'I, I8 offer paths of low impedance for the alternating currents. The plate battery I4 is tapped on the points I5 and I6, to which the auxiliary electrode I0 and the screen grid 'I respectively are joined. The additional grid 9 is negatively charged from the tap I3 of the grid battery I2. Preferably the tapping points I3 and I5 are variable in order to allow the proper adjustment of the internal resistance of the tube.

It is understood, that the grid 9 may also be omitted or without any battery connection, as already stated, thereby resulting in a free floating grid. rThe latter arrangement is shown in Fig. 3, the auxiliary grid 9 being shown as not having a lead-in conductor connection thereto. Otherwise the circuit connections may be the same as in Fig. 1.

In order to simplify the wiring and to save lead-in wires it is proposed to connect the auxiliary electrode to the screen grid and/or the additional grid 9 to the cathode. The connections may be made either within the envelope or within the socket of the tube. One embodiment of such tube is shown in Fig. 2y wherein both connections are made. 3U is the evacuated envelope containing the indirectly heated cathode 3| and the heater 32. The grid 33 is the control electrode, 34 the screen grid, 35 a perforated anode, 36 an additional grid and 31 the auxiliary electrode. The cathode 3l is linked to the grid 36 by a wire 39 and the lead 38 connects the auxiliary electrode 31 to the screen grid 34. The circuit connections are otherwise the same as in Fig. 1.

Although several modifications of the present invention have been described, it is not limited thereto since many changes may suggest themselves to those skilled in the art.

Having now described my invention, what I claim as new and desire to secure by Letters Patent of the United States, is:

1. A thermionic device comprising a cathode and a perforated anode, a plurality of grid electrodes interposed between said cathode and anode, one of said grid electrodes having a signal potential applied thereto, and means positioned on that side of the anode remote from the cathode for producing a negative space charge externally of the anode comprising at least one `auxiliary electrode which is maintained at a constant potential irrespective of the signal potential.

2. A thermionic device comprising a cathode and a perforated anode, a signal control grid and a screening grid interposed between said cathode and anode, said control grid having a signal potential applied thereto, and means positioned on that side of the anode remote from the cathode for producing a negative space charge externally of the anode comprising an auxiliary grid electrode which is maintained at a negative constant operating potential with respect to the cathode irrespective of the signal potential.

3. A thermionic device comprising a cathode and a perforated anode, a signal control grid and a screening grid interposed between said cathode and anode, and means positioned on that side of the anode remote from the cathode for producing a negative space charge externally of the anode comprising an auxiliary electrode which is maintained at a negative constant oper ating potential with respect to the cathode and a second auxiliary electrode which is maintained at a positive constant operating potential, said last named electrode being positioned on that side of the rst auxiliary electrode which is remote from the cathode.

4. A thermionic device comprising an evacuated envelope, a cathode and a perforated anode mounted therein, a grid electrode positioned adjacent the cathode and a second grid electrode positioned adjacent the anode, both said grid electrodes being interposed in the space between said cathode and anode, and a pair of electrodes mounted on that side of the anode remote from the cathode, one being directly connected to the cathode and the other being directly connected to said second grid electrode which is adjacent the anode.

5. A thermionic device comprising an evacuated envelope, an indirectly heated cathode and a perforated anode mounted therein, a signal control grid positioned adjacent the cathode and a screening grid positioned adjacent the anode, both said grids being interposed in the space between said cathode and anode, and a pair of auxiliary electrodes mounted on that side of the anode remote from the cathode, the one immediately adjacent the anode being in the form of a grid and directly connected Within the envelope to the cathode and the other electrode being in the form of a plate and directly connected Within the envelope to the screening grid.

6. In combination, a thermionic tube having a cathode, a control grid, a perforated anode and an auxiliary plate electrode positioned within the tube in the order named, an input circuit connected between the control grid and cathode, an output circuit including a source of potential connected between the perforated anode and cathode, and a direct electrical connection from an intermediate point on said source of potential to the auxiliary plate electrode.

7. In combination, a thermionic tube having a cathode, a control grid, a screen grid, an anode and a pair of auxiliary electrodes positioned within the tube in the order named, an input circuit connected between the control grid and cathode, an output circuit including a source of potential connected between the anode and cathode, and direct electrical connections from intermediate points on said source of potential to the screen grid and to one of the auxiliary electrodes, and a negative potential with respect to the cathode applied to the second auxiliary electrode.

8. In combination, a thermionic tube having a cathode, a control grid, a screen grid, a perforated anode and a pair of auxiliary electrodes positioned Within the tube in the order named, an input circuit connecte-d between the control grid and cathode, an output circuit connected between the anode and cathode, said output circuit including a source of potential with its maximum potential applied to the anode, and direct adjustable connections from the screen grid and the second auxiliary electrode to points on said potential source of lesser potential, and a constant potential with respect to the cathode applied to the rst auxiliary electrode.

9. In combination, a thermionic tube having a cathode, a control grid, a screen grid, a perforated anode and a pair of auxiliary electrodes positioned within the tube in the order named, an input circuit connected between the control potential source of lesser potential, a source of biasingv potential included in the input circuit, and a direct adjustable connection from the rst auxiliary electrode to the biasing potential source.

GNTHER JOBST. 

